1. Field of the Invention
The present invention relates to a magnetic recording medium on which a data track area and a servo pattern area are formed.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. H11-161944 discloses a magnetic disk installed in a magnetic disk apparatus as an example of a magnetic recording medium of this type. As shown in FIGS. 7 and 8 of this publication, this magnetic disk has a plurality of types of convex/concave patterns formed on a substrate made of glass or the like, with such convex/concave patterns being covered with a magnetic film. A data zone, in which convexes (lands) and concaves (grooves) for data recording are formed along a direction of travel of a head slider (that is, a circumferential direction), and a servo zone, in which control signals such as servo signals and the like are recorded by convexes and concaves, are formed on the magnetic disk. On this type of magnetic disk, the fly height of the head slider on the magnetic disk is reduced in parts where the area ratio of concaves to convexes is high. Accordingly, on this magnetic disk, convexes and concaves are formed by inverting a convex/concave pattern of a servo zone of a normal magnetic disk (patterned medium) to reduce the area ratio of the concaves to convexes in the servo zone and thereby reduce the fly height. By doing so, compared to a normal magnetic disk, it is possible to suppress the fluctuation in the fly height of the head slider when the head slider passes the data zone and passes the servo zone.
However, the above conventional magnetic disk has the following problem. That is, on the conventional magnetic disk, fluctuation in the fly height of the head slider is suppressed by reducing the area ratio of the concaves to the convexes. For such a disk, the types of convex/concave patterns differ between the data zone and the servo zone. For this reason, it is extremely difficult to make one area ratio of concaves in the data zone to convexes match another area ratio of concaves in the servo zone to convexes by inverting the convex/concave pattern of a servo pattern on a normal magnetic disk. Accordingly, with the conventional magnetic disk where the area ratio of the concaves to the convexes is reduced, there is the problem that it is difficult to considerably reduce the fluctuation in the fly height of the head slider.
On the other hand, the present inventors have developed a technique that considerably suppresses the amount of fluctuation in the fly height of a head slider by using a construction where the surface of a magnetic disk is flattened by embedding a nonmagnetic body inside the concaves of the data track area (data zone) and the servo pattern area (servo zone) so that concaves are not formed in the surface of a magnetic disk or only extremely shallow concaves are formed. More specifically, as shown in FIG. 14, first, convex/concave patterns P1 to P4 for forming a data track area A1 and a servo pattern area A2 (see FIG. 16) are formed by a ferromagnetic body 15 on a multilayer structure 2 (substrate) in which a glass substrate, a base layer, a soft magnetic layer, an oriented layer, and the like are formed in layers. Next, as shown in FIG. 15, a nonmagnetic body 16 is formed by sputtering so as to cover the convex/concave patterns P1 to P4. After this, as shown in FIG. 16, the nonmagnetic body 16 is etched in the data track area A1 until the surface of the ferromagnetic body 15 is exposed from the nonmagnetic body 16. By doing so, the surface of the magnetic disc is flattened.
However, by further investigating the above technique they had developed themselves, the present inventors discovered the following problems. That is, in their own technique, as shown in FIG. 16, in parts (such as a preamble area Ap and an address area Aa) of the convex/concave patterns P2, P3 whose formation pitch is larger (i.e., the concaves are wider) than the formation pitch of the convex/concave pattern P1 of the data track area A1, the nonmagnetic body 16 is more easily etched than in the data track area A1, so that the surface of the nonmagnetic body 16 in the convex/concave patterns P2, P3 becomes lower than the surface of the nonmagnetic body 16 inside the convex/concave pattern P1. Therefore, as shown in FIG. 17, an average height H12 from the surface of the multilayer structure 2 in the preamble area Ap and the address area Aa becomes lower than an average height H11 in the data track area A1, resulting in the fly height in the preamble area Ap and the address area Aa being lower than in the data track area A1. Also, as shown in FIG. 16, in parts (such as a burst area Ab) of the convex/concave pattern P4 where the formation pitch is smaller than that of the convex/concave pattern P1 (i.e., the concaves are narrower), the nonmagnetic body 16 is more difficult to etch than in the data track area A1, so that in some cases the nonmagnetic body 16 is left on the convexes of the convex/concave pattern P4. Therefore, as shown in FIG. 17, an average height H13 of the burst area Ab becomes higher than the average height H11 of the data track area A1, resulting in the fly height of the burst area Ab becoming large relative to that of the data track area A1. Accordingly, for a magnetic disk that has the preamble area Ap and the address area Aa, where the fly height is low, and the burst area Ab, where the fly height is high, inside the servo pattern area, there is the problem of increased fluctuation in the fly height per revolution of the magnetic disk. It should be noted that even when only an area where the fly height is low or only an area where the fly height is high is present inside the servo pattern area, there is still the problem of increased fluctuation in the fly height per revolution of the magnetic disk.
The present invention was conceived to solve the problem described above and it is a principal object of the present invention to provide a magnetic recording medium that can considerably suppress fluctuation in the fly height of a head slider.